Emergence of blaNDM-1, blaNDM-5, blaKPC-2 and blaIMP-4 carrying plasmids in Raoultella spp. in the environment

To date, carbapenem-resistant Enterobacteriaceae have been found predominantly in clinical settings worldwide. Raoultella belongs to the Enterobacteriaceae family which can cause hospital-acquired infections, and carbapenem-resistant Raoultella spp. (CRR) is sporadically reported in the environment. We investigated the distribution and underlying resistance mechanisms of CRR in a wastewater treatment plant (WWTP) from eastern China between January 2018 and February 2019. A total of 17 CRR were isolated from 324 environmental samples, including Raoultella ornithinolytica (n = 15) and Raoultella planticola (n = 2). The detection of CRR was more frequent in the water inlet compared to anaerobic tank, aerobic tank, sludge thickener, activated sludge, mud cake storage area, and water outlet, and CRR was detected in mud cake stacking area. All CRR were resistant to imipenem, meropenem, ampicillin, piperacillin-tazobactam, cefotaxime, ceftazidime, trimethoprim-sulfamethoxazole and fosfomycin. Four different carbapenemase genes were identified, including bla(KPC-2) (n = 13), bla(NDM-1) (n = 8), bla(NDM-5) (n = 1), bla(IMP-4) (n = 1). Interestingly, isolated R. ornithinolytica from the WWTP were closely related to those reported from human samples in China. Plasmid analysis indicated that IncFII(Yp), IncP6, and IncU mediated bla(KPC-2) spread, IncX3 and IncN2 mediated bla(NDM) spread in the environment. The core structure of the Tn3-ISKpn27-bla(KPC-2)-ISKpn6, ISAba125-bla(NDM)-ble(MBL)-trpF-dsbD were identified. The study provides evidence that Raoultella spp. may spread alarming carbapenem resistance in the environment and, therefore, the continuous surveillance for carbapenem resistance in the WWTP should be conducted, especially sludge.

Automated summary

This study investigated the distribution and resistance mechanisms of carbapenem-resistant Raoultella spp. (CRR) in a wastewater treatment plant (WWTP) in eastern China. The results showed that CRR were mainly found in the water inlet and mud cake stacking area of the WWTP, with a higher detection rate in the water inlet. All CRR isolates were resistant to multiple antibiotics and various carbapenemase genes were identified. Interestingly, R. ornithinolytica isolates from the WWTP were closely related to those from human samples in China. Plasmid analysis revealed the transmission routes and core structures of carbapenemase genes in the environment.